Fuel Cell Assembly Comprising a Plurality of Microcells

ABSTRACT

The present invention relates to fuel cell assembly having a plurality of microcells, and to methods of assembling fuel cell assemblies from microcells. A plurality of microcells is circumferentially spaced around a central member. Each microcell comprises an inner current collector having one or more microchannels formed therein, a proton exchange membrane surrounding said inner current collector, and an outer current collector disposed on the outside of said proton exchange membrane. A first electrical connector disposed at a first end of the fuel cell assembly electrically connects to the inner current collectors of said microcells. A second electrical connector disposed at a second end of the fuel cell assembly electrically connects to the outer current collectors of the microcells. In one embodiment, inner and outer seals are disposed in spaced relation to one another adjacent the first end of said fuel cell assembly. A gap between said inner and outer seals is in fluid communication with the microchannels in the microcells to provide a pathway for introduction of a gaseous reactant into said microchannels of said microcells.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication 60/988,906 filed Nov. 19, 2007, which is incorporated hereinby reference.

BACKGROUND

The present invention relates generally to electrochemical cell and fuelcell technology and, more particularly, to fuel cell modules includingmicrofiber fuel cells or microtubular fuel cells, also known asmicrocells.

A fuel cell is a type of electrochemical energy device similar to abattery. A fuel cell includes a cathode and an anode separated by amembrane. A fuel, such as hydrogen, is supplied to the anode side of thefuel cell, while an oxidant, such as oxygen, is supplied to the cathodeside of the fuel cell. The hydrogen splits into positive hydrogen ionsand negatively-charged electrons. The membrane separator allows thepositively-charged ions to pass through to the cathode side of the fuelcell. The negatively-charged electrons, however, must travel through anelectric circuit to the cathode, thus creating an electrical current. Atthe cathode side of the fuel cell, the electrons and positively-chargedhydrogen ions combine with oxygen to form water.

Microfiber fuel cells or microtubular fuel cells, also calledmicrocells, represent one promising fuel cell technology. A microcell isa fiber-like fuel cell wherein the inner current collector, membraneseparator and catalyst layers are extruded as a single fiber. The fibersmay range in size from a few hundred to several thousand microns. Oneadvantage of the fuel cell topology is that is achieves the highestpossible MEA surface area to volume ratio, resulting in compact fuelcells. Another advantage is its scalability. The microcells can beassembled together in bundles to form units called unicells. Theunicells can be further bundled to form larger units called modules.

SUMMARY

The present invention relates to fuel cell modules and to methods ofassembling fuel cell modules from microcells. A plurality of microcellsare bundled together to form units called unicells. A plurality of theunicells are, in turn, bundled together to form the fuel cell module.Novel ways of assembling unicells and fuel cell modules are described.

In one exemplary embodiment, a fuel cell assembly comprises a centralmember extending along a longitudinal axis of the fuel cell assembly,and a plurality of cylindrical microcells disposed around the centralmember. Each microcell comprises an inner current collector, innercatalyst layer (e.g., anode), a proton exchange membrane surroundingsaid inner current collector and inner catalyst layer; an outer catalystlayer (e.g., cathode), and an outer current collector disposed on theoutside of said proton exchange membrane and outer catalyst layer. Afirst electrical connector is disposed at a first end of the fuel cellassembly and is electrically connected to said inner current collectorsof said microcells. A second electrical connector is disposed at asecond end of said fuel cell assembly and is electrically connected tosaid outer current collectors of said microcells. Inner and outer sealsdisposed in spaced relation to one another adjacent the first end ofsaid fuel cell. The seals define a gap that is in fluid communicationwith said microchannels in the microcells to provide a pathway for theintroduction of a gas reactant into the microchannels.

In one exemplary embodiment, a fuel cell assembly comprises a centralmember extending along a longitudinal axis of the fuel cell assembly,and a plurality of cylindrical microcells disposed around the centralmember. Each microcell comprises an inner current collector (e.g.,anode), a proton exchange membrane surrounding said inner currentcollector; and an outer current collector (e.g., cathode) disposed onthe outside of said proton exchange membrane. A firstelectrically-conductive, flexible connector is disposed at a first endof the fuel cell module and is electrically connected to the innercurrent collectors of the microcells. A second electrically-conductive,flexible connector is disposed at the second end of the fuel cell and iselectrically connected to the outer current collectors of themicrocells.

In another exemplary embodiment, a fuel cell assembly comprises anelectrically conductive central member extending along a longitudinalaxis of the fuel cell assembly, and a plurality of cylindricalmicrocells disposed around the central member. Each microcell comprisesan inner current collector (e.g., anode), a proton exchange membranesurrounding said inner current collector; and an outer current collector(e.g., cathode) disposed on the outside of said proton exchangemembrane. First and second electrical connectors are disposed atopposite ends of the fuel cell assembly. The first electrical connectoris coaxially aligned with the central member and is electricallyisolated from the central member. The inner current collectors of themicrocells electrically connect to the first electrical connector. Thesecond current collectors of the microcells electrically connect to thesecond electrical connector.

In another exemplary embodiment, a fuel cell assembly comprises acentral member extending along a longitudinal axis of the fuel cellassembly, and a plurality of microcells disposed about the centralmember to form a bundle. Each microcell comprises an inner currentcollector, inner catalyst layer (e.g., anode), a proton exchangemembrane surrounding the inner current collector and inner catalystlayer; an outer catalyst layer (e.g., cathode), and an outer currentcollector disposed on the outside of said proton exchange membrane. Anelectrically conductive member winds around the bundle of microcells tohold the microcells in contact with the central member. The electricallyconductive member has a substantially planar surface disposed toward themicrocells and in electrical contact with the outer current collectorsof the microcells so as to electrically connect the outer currentcollectors of individual microcells. The outer current collector maywind helically around the microcell. The width of the wrap is preferablygreater than the distance between two successive windings (i.e., thepitch) of the outer current collector.

In another exemplary embodiment, a fuel cell assembly comprises acentral member extending along a longitudinal axis of the fuel cellassembly, and a plurality of cylindrical microcells disposed around thecentral member. Each microcell comprises an inner current collector(e.g., anode), a proton exchange membrane surrounding the inner currentcollector; and an outer current collector (e.g., cathode) disposed onthe outside of said proton exchange membrane. The first currentcollectors of the microcells electrically connect to a first electricalconnector disposed at a first end of the fuel cell assembly. At leastone conductive strip electrically connects a plurality of the firstcurrent collectors to one another and to the first electrical connector.The second current collectors electrically connect to a secondelectrical connector disposed at a second end of the fuel cell assembly.

In another exemplary embodiment, a fuel cell module comprises at leastone deformable bulkhead having a plurality of holes formed therein. Aplurality of fuel cell elements extend through corresponding first holesin the bulkhead. At least one compression member applies a radiallyinward compressive force to the bulkhead to help form a gas-tight sealbetween the bulkhead and the plurality of fuel cell elements. The fuelcell module may further comprise a housing circumferentially surroundingthe fuel cell elements with a bulkhead at opposing ends of the housing,and means to press the bulkheads into contact with the first and secondends respectively of the housing to help form and/or maintain agas-tight seal between the housing and the bulkheads.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a fuel cell module 10

FIG. 2 is a perspective view of an exemplary microcell.

FIG. 3 is a perspective view of an exemplary unicell.

FIG. 4 is a longitudinal section view at a first end of an exemplaryunicell.

FIG. 5 is a cross section of a unicell taken through line 4-4 of FIG. 3.

FIG. 6 illustrates an exemplary method for electrically connecting innercurrent collectors of a unicell.

FIG. 7 is a longitudinal section view of another exemplary unicell withflexible connectors.

FIG. 8 is an exploded perspective view of a fuel cell module.

FIG. 9 is a side elevation view of a fuel cell module.

FIG. 10 is a side elevation view of another exemplary fuel cell module.

FIG. 11 is a schematic diagram illustrating the electrical connectionsbetween unicells at a first end of a fuel cell module.

FIG. 12 is a schematic diagram illustrating the electrical connectionsbetween unicells at a second end of a fuel cell module.

DETAILED DESCRIPTION

The present invention is directed to a hydrogen fuel cell module 10. Thefuel cell module 10 comprises a plurality of individual microcells 100(FIG. 2). A plurality of the microcells 100 are bundled to form unitsreferred to herein as unicells 200 (FIGS. 3-5). A plurality of theunicells 200 are then bundled together to form the fuel cell module 10(FIGS. 1 & 7-9).

FIG. 2 illustrates an exemplary microcell 100. The basic structure andassembly of the microcell 100 is described in U.S. Pat. Nos. 5,916,514;5,928,808; 5,989,300; 6,004,691; 6,338,913; 6,399,232; 6,403,248;6,403,517; 6,444,339; 6,495,281; 6,884,539; and 7,229,712; and U.S.Patent Publ. Nos. 2007/0243439 and 2005/0181269 which are incorporatedherein by reference. For convenience, a brief description of themicrocell 100 is provided herein.

The microcell 100 comprises an inner current collector 102, a firstcatalyst layer 104, a proton exchange membrane (PEM) 106, a secondcatalyst layer 108, and a outer current collector 110. The microcell 100could also optionally include a carbon fiber layer between the secondcatalyst layer 108 and outer current collector 110. The inner currentcollector 102 comprises an electrically conductive wire that extendslongitudinally through the microcell 100. In the exemplary embodiments,the inner current collector 102 comprises a layered structure of copper,titanium, and niobium, but such is not required. The inner currentcollector 102 may be exposed at the ends of the microcell 100, ifdesired. The inner current collector 102 may have a plurality ofmicrochannels 112 formed therein to permit the flow of air or oxygenthrough the microcell 100. The first catalyst layer 104, PEM 106, andsecond catalyst layer 108 surround the inner current collector 102. Thefirst and second catalyst layers 104, 108 may, for example, compriselayers of a platinum catalyst. The outer current collector 110 windsaround the second catalyst layer 108. In one embodiment, the outercurrent collector 110 is a titanium wire wound at a uniform pitch P,which may be substantially the diameter of outer current collector 110or may be larger. A microcell 100 is typically in the range of 200microns to 3 millimeters in diameter.

FIGS. 3-5 illustrate an exemplary unicell 200. A unicell 200 is a fuelcell assembly comprising a plurality of microcells 100 bundled together.The unicell 200 is elongated and cylindrical in form with a first end201 and a second end 203. In general, one of the ends, 201,203 functionsas an anodic end, while the other end functions as a cathodic end. Forsimplicity of description, it will be assumed that end 201 functions asthe cathodic end and end 203 functions as anodic end; however, it shouldbe understood that the unicell 200 could easily have an oppositeanodic/cathodic configuration.

In the illustrated embodiment, there are ten microcells 100 in a unicell100, although those skilled in the art will appreciate that any numberof microcells 100 could be used. The microcells 100 arecircumferentially spaced around a central member 203. The central member203 may comprise a solid rod or a hollow tube, with either made of anelectrically-conductive material or an electrically non-conductivematerial. The tube may be 1/16 inches to ½ inches in diameter and 1-30cm in length. In one embodiment, the central member 203 is hollow andfunctions as a heat exchange tube through which a coolant fluid flows.The central member 203 may be fabricated from the same material as innercurrent collector 102.

A pair of spaced-apart seals 204, 206 is disposed at each end of theunicell 200. The seals 204, 206 are preferably formed by a moldedelectrically nonconductive epoxy. A gap 208 is formed between the innerseals 206 and outer seals 204 at each end 201, 202 of the unicell 200.The inner current collectors 102 of the microcells 100 extend throughthe inner seals 206, across gaps 208, and at least partially through theouter seals 204. The inner current collectors 102 of the microcells 100are exposed within the gap 208 so that one of the gaseous reactants(e.g., air) can enter into the microchannels 112 at one end of themicrocells 100 and exit at the opposite end. The first catalyst layer104, PEM 106, and second catalyst later 108 may terminate at the innerseal 206.

A conductive wrap 212 winds in helical fashion around the microcells 100and holds the microcells 100 to electrically connect the outer currentcollectors 110 of the microcells 100. The conductive wrap 212 also holdsthe microcells 100 in close contact with the central member 203 so as toprovide good electrical contact between the outer current collectors 110of the microcells 100 and the central member 203. The conductive wrap212 preferably includes a substantially flat surface in contact with theouter current collectors 110 of the microcells 100. The width W of thisflat surface is preferably greater than the distance betweencorresponding points on two consecutive windings (i.e., the pitch) ofthe outer current collector 110. Conductive wrap 212 may be wrappedaround the microcell bundles so that consecutive windings of wrap 212 donot touch. This arrangement provides interstitial spaces betweenwindings that allow gases to flow around the exterior of microcells 100.In one embodiment, the wrap 212 is fabricated from the same material asinner current collector 102.

Longitudinally spaced insulators 214 may be disposed around the centralmember 203 at end 201, 203 of the unicell 200 to space and electricallyisolate the inner current collectors 102 from the central member 203.More particularly, insulators 214 may be located at each seal 204, 206so that the seals 204, 206 encapsulate and hold the insulators 214. Inaddition, an outer retention member 216 may be disposed around themicrocells 110 in general alignment with insulators 214. The insulator214 and retention member 216 may comprise a non-conductive heat shrinktubing, or other appropriate material. Preferably, inner insulator 214and retention member 216 are significantly shorter in longitudinallength than the respective seals 204, 206 and disposed toward the end ofthe respective seal 204, 206 closest to gap 208. The inner insulator 214and retention member 216 may be fully encapsulated by the materialforming seals 204, 206, but may extend therefrom in some embodiments.

In the exemplary embodiment shown in FIGS. 3-5, the central member 203terminates within the outer seal 204 at a first end 201 of the unicell200 and protrudes at the second end 202 of the unicell 200. In thisembodiment, a separate stub member 210 protrudes from the outer seal 204at the first end 201 of the unicell 200. The outer seal 204 mechanicallyjoins the stub member 210 with the central member 203 while at the sametime electrically isolating the stub member 210 from the central member203. The stub member 210 functions as a first electrical connector andthe inner current collectors 102 of the microcells 100 are electricallyconnected to the stub member 210. The protruding end of the centralmember 203 at second end 202 of the unicell 200 functions as a secondelectrical connector. The protruding ends of the central member 203and/or stub member 210 may be externally threaded if desired. Inembodiments where the central member 203 comprises a heat exchange tube,the stub member 210 may have an axial opening 211 in fluid communicationwith the hollow longitudinal passage 203 p of central member 203. Afluid passage 205 may be formed in the outer seal 204 at the first end201 of the unicell 200 to allow coolant fluid to flow from the stubmember 210 into the central member passage 203 p.

FIG. 6 illustrates one method of electrically connecting the innercurrent collectors 102 of the microcells 100 to the stub member 210. Theinner current collectors 102 are connected to a conductive strip 220 byany suitable means, such as by adhesive, heat welding, ultrasonicbonding, soldering, crimping, or other suitable techniques. In oneexemplary embodiment, five inner current collectors are connected toeach of two conductive strips 220, each made of copper. The conductivestrips 220 are then formed around and electrically connected to stubmember 210, such as by soldering.

In another exemplary embodiment of the unicell 200 shown in FIGS. 7A-7B,flexible connectors 222, 224 are utilized for making the electricalconnections at the ends of unicell 100. For example, inner currentcollectors 102 are electrically connected to one or more first flexibleconnectors 222 at the first end 201 of the unicell 200. This connectionmay be by any suitable method, such as the method described above withrespect to conductive strip 220. Outer current collectors 110 and/or thecentral member 203 electrically connect to one or more second flexibleconnectors 224 at the second end 202 of the unicell 200. The flexibleconnectors 222,224 may comprise braided wires, although any other formof flexible connection known in the electrical arts may be used. In oneembodiment, two or more flexible connectors 222, 224 are disposed ateach end 201, 202, respectively. With such connections, central member203 may protrude at both ends 201, 202 of the unicell 200, withprotruding ends of central member 203 externally threaded or otherwiseconfigured to assist in mechanically securing the unicells 200. Suitablemeasures should be taken to electrically insulate the central member 203from the inner current collectors 102 and associated flexible connector222, such as by providing an electrically insulating material layer 226there between at the first end 201 of the unicell 200.

The unicells 200 are bundled together to form fuel cell modules 10. Afuel cell module typically comprises many unicells 100. The number ofunicells 200 in a fuel cell module could vary from 1 to approximately1000, but more typically is in the range of twenty-five to a hundred.The fuel cell module 10 will typically have a diameter in the range of0.25 inches to 12.0 inches. Those skilled in the art will appreciatethat the number of unicells 200 in a module 10 is not material and ingeneral is dictated by factors such as size, weight, and desired poweroutput.

FIGS. 8-9 illustrate the assembly of an exemplary fuel cell module 10.The exemplary fuel cell module 10 includes a housing 12. The exemplaryhousing 12 is generally cylindrical and comprises five housing sections14, 16, 18, 20, 22; four bulkheads 24, 26, 28, 30; and two end plates32, 34. The housing sections 14, 16, 18, 20, 22 can be made from a widerange of materials including metals, fiberglass, and carbon-reinforcedepoxy composites. For ease of reference, housing sections 14, 22 arereferred to as the end sections, housing sections 16 and 20 are referredto as the intermediate sections, and housing section 18 is referred toas the center section. The bulkheads 24, 26, 28, 30 are disposed betweenrespective housing sections and may be similar to or slightly larger indiameter than housing sections 14, 16, 18, 20, 22. Bulkheads 24, 26, 28,30 are made from a compressible material that is also electricallynonconductive, such as silicone or fluoro-silicone. Compression members,such as clamps 36, are disposed around bulkheads 24, 26, 28, 30 toradially compress bulkheads 24, 26, 28, 30. End plates 32, 34 aredisposed at opposing ends of the fuel cell module 10 and may be made ofa conductive material, such as a metal. A gasket (not shown) may bedisposed between the endplates 32, 34 and respective housing sections14, 22 to provide a fluid tight seal. The entire assembly islongitudinally held together by tension rods 38 that pass through endplates 32, 34. Tension rods 38 may be threaded at each end and securedby threaded connectors. When the threaded connectors are tightened, theend caps 32, 34 apply an axially compressive force that forces housingsections 14, 16, 18, 20, 22 and bulkheads 24, 26, 28, 30, together so asto form seals therebetween.

As shown in FIG. 8, bulkheads 24, 26, 28, 30 have a plurality ofopenings 40 formed therein. The unicells 200 extend through the openings40 in the bulkheads 24, 26, 28, 30 so that the ends of the unicells 100terminate within the end sections 14, 22 of housing 12. Seals 204, 206of the unicells 200 align with the bulkheads 24, 26, 28, 30. When thebulkheads are radially compressed, a gas-tight seal is formed betweenthe bulkheads 24, 26, 28, 30 and the seals 204, 206. The seal formed issufficient to prevent the undesired flow of the gaseous reactantsthrough the sealed sections at the normal operating pressures of 15-20psi. The openings 40 are preferably slightly undersized with respect tothe size of the corresponding seals 204, 206 to provide an interferencefit. If desired, one or more openings 40 may of a different size, suchas a larger central opening for acceptance of an input/output line, asdiscussed further below. The openings 40 are advantageously arranged ina close-packed configuration, and the bulkheads 24, 26, 28, 30 areadvantageously identical, although neither condition is required for allembodiments.

The opposing ends of the housing sections 16, 18, 20 seat against theopposing faces of respective bulkheads 24, 26, 28, 30. A first end ofhousing sections 14, 22 seats against a respective end plate 32, 34 anda second end of housing sections 14, 22 seats against a respectivebulkhead 24, 30. When the tension rods 38 are tightened, the entireassembly is axially compressed to form gas-tight seals between the endsof the housing sections 14, 16, 18, 20, 22; the bulkheads 24, 26, 28,30; and end plates 32, 34.

The bulkheads 24, 26, 28, 30 divide the interior of the fuel cell module10 into five chambers. The three center chambers 16 c, 18 c, 20 c serveas gas chambers for gas reactants. The outer chambers 14 c, 22 c mayserve as fluid chambers for a coolant. Of course, additional bulkheadsand housing sections may be included, so as to form additionalchamber(s) if desired. Also, those skilled in the art will appreciatethat the housing may include fewer than five chambers in someembodiments.

A gas inlet 42 for a first gas reactant is disposed in housing section16 and a corresponding gas outlet 44 is disposed in housing section 20.A gas inlet 46 and gas outlet 48 for the second gas reactant may bedisposed along the longitudinal axis of the fuel cell module 10 andextend into housing section 18. In this embodiment, the endplates 32,34, as well as the bulkheads 24, 26, 28, 30 include a central openingfor the gas inlet 46 and gas outlet 48 respectively. The gas inlet 46may comprise a tube that extends along the axis of the fuel cell module10 through endplate 32 and bulkheads 24, 26 and terminates in thecentral gas chamber 18 c. Similarly, the gas outlet 48 may comprise atube that extends along the axis of the fuel cell module 10 through theendplate 34 and bulkheads 30, 28, and terminates in the central gaschamber 18 c. Alternatively, or in addition thereto, gas inlet 46 andgas outlet 48 may connect to the central gas chamber 18 c via side entrythrough the periphery of housing section 18, advantageously towardopposite ends of the central housing section 18. Coolant, such asde-ionized water or air, is fed into chamber 14 c, flows along thelongitudinal passages 203 p of the unicells 200, and into chamber 22 c,from which it is exhausted, typically for cooling and recirculation.

During operation, a first gas reactant, such as oxygen or air, entersthe gas inlet 42 at one end of the fuel cell module 10 into gas chamber16 c, enters the microchannels 112 of the microcells 110 at gap 208,flows through the microchannels 112 into a gas chamber 20 c at theopposite end of the fuel cell module 10, and exits the fuel cell module10 through the gas outlet 44. A second gas reactant, such as hydrogen,enters gas inlet 46, fills a central gas chamber 18 c surrounding thecentral portion of unicells 200, and exits the gas outlet 48. In apreferred embodiment, tubular sleeves 250 (shown in FIG. 3) can beplaced around each unicell 200 to facilitate an axial flow of gas alongeach unicell 200. The tubular sleeves 250 can be made, for example, froma heat shrink material. The hydrogen gas in the central gas chamber 18 centers the tubular sleeve 250 at an end adjacent to the gas inlet 46 andexits the tubular sleeve 250 at an end adjacent the gas outlet 48. Forsuch an arrangement, an additional bulkhead 27 and housing section 17may be added on the inlet side of the chamber 18 c as shown in FIG. 10so as to force the gas to flow into to the tubular sleeves 250. In thisembodiment, the tubular sleeves 250 may protrude slightly into housingsection 17 so that the hydrogen can enter the ends of the tubular selves250.

The operation of the fuel cell module 10 may result in the generation ofwater or other liquid in reaction chamber 18 c, and drain 56 is providedfor removing such. In addition, the operation of the fuel cell module 10may result in the generation of significant heat. As previously noted,the central member 203 may function as a heat exchange tube to aid inremoving this heat. Alternatively or in addition thereto, dedicatedcooling tubes (not shown) may be interposed in the array of unicells200. A suitable coolant may be introduced into the central member 203and/or cooling tubes to absorb and carry off some of the heat producedby the microcells 100 during operation. Accordingly, the central member203 and/or cooling tubes are advantageously in fluid communication withchambers 14 c, 22 c at each end of fuel cell module 10. A fluid inlet 52may be disposed in the end section 14 of the housing 12 and acorresponding fluid outlet 54 may be disposed in end section 22. Aliquid coolant, such as de-ionized water, enters fluid chamber 14 cthrough fluid inlet 52, flows through the central member 203 and/orcooling tubes into the fluid chamber 22 c, and exits the fuel cellmodule 10 through fluid outlet 54.

The unicells 200 are electrically interconnected in chamber 14 c, 22 c.The interconnections may be arranged so that the unicells 200 areconnected in series, are connected in parallel, or in any suitablecombination thereof. The unicell interconnections may be made using theflexible connectors 222, 224, or by using conductive plates mechanicallyand electrically connected to the central members 203 and stubs 210, orby a combination thereof, or by any other suitable electricalinterconnection means known in the electrical arts. When compressiblebulkheads are employed, care should be taken to allow for possiblerelative movement between the unicells 200 as the bulkheads areperipherally compressed.

FIGS. 11 and 12 illustrate an exemplary method of interconnectingunicells 200 in a fuel cell module 10. As shown in FIGS. 11 and 12, theindividual unicells 200 are interconnected by conductive plates 260 thatconnect the central members 203 and/or stubs 210 of the unicells 200.The conductive plates 260 may be held in place by nuts (not shown) thatthread onto the ends of the central members 203 and/or stubs 210 of theunicells 200. The orientation of the unicells 200 is illustrated bysolid and dashed lines. The unicells 200 are organized into groups ofthree unicells 200. The three unicells 200 in each group are connectedin parallel. All of the groups are then connected in series. Of course,the number of unicells 200 in each group can be varied depending on thedesired current and/or voltage.

The present invention may be carried out in other specific ways thanthose herein set forth without departing from the scope and essentialcharacteristics of the invention. Further, the various aspects of thedisclosed device and method may be used alone or in any combination, asis desired. The disclosed embodiments are, therefore, to be consideredin all respects as illustrative and not restrictive, and all changescoming within the meaning and equivalency range of the appended claimsare intended to be embraced therein.

1. A fuel cell assembly comprising: a central member extending along alongitudinal axis of said fuel cell assembly; a plurality of cylindricalmicrocells circumferentially spaced around said central member, eachsaid microcell comprising an inner current collector having one or moremicrochannels formed therein, a proton exchange membrane surroundingsaid inner current collector, and an outer current collector disposed onthe outside of said proton exchange membrane; a first electricalconnector disposed at a first end of said fuel cell assembly andelectrically connected to said inner current collectors of saidmicrocells; a second electrical connector disposed at a second end ofsaid fuel cell assembly and electrically connected to said outer currentcollectors of said microcells; inner and outer seals disposed in spacedrelation to one another adjacent said first end of said fuel cellassembly; and a gap between said inner and outer seals, said gap beingin fluid communication with said microchannels in said microcells toprovide a pathway for introduction of a gaseous reactant into saidmicrochannels of said microcells.
 2. The fuel cell of claim 1 whereinsaid outer current collectors terminate at said inner seal and whereinsaid inner current collectors extend across said gap and terminate atsaid outer seal.
 3. The fuel cell of claim 1 wherein said central memberis electrically conductive.
 4. The fuel cell of claim 3 wherein saidinner current collectors of said microcells are electrically isolatedfrom said central conductor and wherein said outer current collectors ofsaid microcells are in electrical contact with said central member. 5.The fuel cell of claim 4 wherein said first electrical connectorcomprises an electrically conductive stub member coaxially aligned withand electrically isolated from said central member.
 6. The fuel cell ofclaim 5 further comprising a conductive strip electrically connecting aplurality of inner current collectors of individual microcells with oneanother and with said stub member.
 7. The fuel cell of claim 6 furthercomprising an electrically conductive wrap wound around said microcellsto hold said microcells in contact with said central member and toprovide electrical connection between said outer current collectors ofindividual microcells.
 8. The fuel cell of claim 6 wherein said secondelectrical connector comprises a portion of said central memberprotruding from said second end of said fuel cell assembly.
 9. The fuelcell of claim 1 wherein said first electrical connector comprise one ormore flexible wires electrically connecting with one or more of saidinner current collectors.
 10. The fuel cell of claim 1 wherein saidsecond electrical connector comprises one or more flexible wireselectrically connecting with one or more of said outer currentcollectors.
 11. A fuel cell assembly comprising: an electricallyconductive central member extending along a longitudinal axis of saidfuel cell assembly; a plurality of cylindrical microcellscircumferentially spaced around said central member, each said microcellcomprising an inner current collector, a proton exchange membranesurrounding said inner current collector, and an outer current collectordisposed on the outside of said proton exchange membrane; a firstelectrical connector disposed at a first end of said fuel cell assemblyand electrically connected to said inner current collectors of saidmicrocells, said first electrical connector being coaxially aligned withand electrically isolated from said central member; and a secondelectrical connector disposed at a second end of said fuel cell assemblyand electrically connected to said outer current collectors of saidmicrocells.
 12. The fuel cell of claim 11 further comprising aconductive strip electrically connecting a plurality of inner currentcollectors of individual microcells with one another and with said stubmember.
 13. The fuel cell of claim 11 further comprising an electricallyconductive wrap wound around said microcells to hold said microcells incontact with said central member and to provide an electrical connectionbetween said outer current collectors of individual microcells.
 14. Thefuel cell of claim 11 wherein said second electrical connector comprisesa portion of said central member protruding from said second end of saidfuel cell assembly.
 15. The fuel cell assembly of claim 11 wherein saidcentral member comprises a heat exchange tube.
 16. The fuel cellassembly of claim 15 wherein said first electrical connector comprises atubular stub in fluid communication with said heat exchange tube.
 17. Afuel cell assembly comprising: a central member extending along alongitudinal axis of said fuel cell assembly; a plurality of cylindricalmicrocells circumferentially spaced around said central member, eachsaid microcell comprising an inner current collector, a proton exchangemembrane surrounding said inner current collector, and an outer currentcollector disposed on the outside of said proton exchange membrane; andan wrap wound around said plurality of microcells; said wrap having asubstantially planar surface disposed toward said microcells and incontact with said outer current collectors of said microcells.
 18. Thefuel cell assembly of claim 17 wherein said wrap is electricallyconductive and electrically connects said outer current collectors toone another.
 19. The fuel cell assembly of claim 17 wherein said centralmember is electrically conductive and wherein said wrap holds said outercurrent collectors of said microcells in contact with said centralmember.
 20. The fuel cell assembly of claim 17 wherein said wrap ishelically wound around said microcells.
 21. The fuel cell assembly ofclaim 20 wherein said outer current collector is wound onto saidmicrocell and wherein said flat surface of said wrap has a width greaterthan pitch of said outer current collector.
 22. A fuel cell assemblycomprising: a central member extending along a longitudinal axis of saidfuel cell assembly; a plurality of cylindrical microcellscircumferentially spaced around said central member, each said microcellcomprising an inner current collector, a proton exchange membranesurrounding said inner current collector, and an outer current collectordisposed on an outside of said proton exchange membrane; a firstelectrical connector disposed at a first end of said fuel cell assemblyand electrically connected to said inner current collectors of saidmicrocells; a conductive strip formed around said first electricalconnector, said conductive strip electrically connecting a plurality ofinner current collectors of individual microcells with one another andwith said first electrical connector; and a second electrical connectordisposed at a second end of said fuel cell assembly and electricallyconnected to said outer current collectors of said microcells.
 23. Thefuel cell assembly of claim 22 wherein said first electrical connectorcomprises a stub member coaxially aligned with said central member. 24.The fuel cell of claim 23 wherein said central member is electricallyconductive.
 25. The fuel cell of claim 24 wherein said inner currentcollectors of said microcells are electrically isolated from saidcentral member and wherein said outer current collectors of saidmicrocells are in electrical contact with said central member.
 26. Thefuel cell of claim 25 further comprising an electrically conductive wrapwound around said microcells to hold said microcells in contact withsaid central member and to provide electrical connection between saidouter current collectors of one or more of said microcells.
 27. The fuelcell of claim 25 wherein said second electrical connector comprises aportion of said central member protruding from said second end of saidfuel cell assembly.
 28. A fuel cell assembly comprising: a centralmember extending along a longitudinal axis of said fuel cell assembly; aplurality of cylindrical microcells circumferentially spaced around saidcentral member, each said microcell comprising an inner currentcollector having one or more microchannels formed therein, a protonexchange membrane surrounding said inner current collector, and an outercurrent collector disposed on the outside of said proton exchangemembrane; a first electrically conductive, flexible connector disposedat a first end of said fuel cell assembly and electrically connected tosaid inner current collectors of said microcells; and a secondelectrically conductive, flexible connector disposed at a second end ofsaid fuel cell assembly and electrically connected to said outer currentcollectors of said microcells.